Preparo do solo em áreas de produ？？o de gr？os, silagem e pastejo: efeito na resistência tênsil e friabilidade de agregados

the understanding and quantification of soil use and management on the soil physical quality are important to develop and select sustainable agricultural systems. the purpose of this study was to evaluate the structural quality of a clayey brazilian oxisol under different production and soil tillage systems by measuring the tensile strength (ts) and to quantify aggregate friability (f). the study was conducted in castro, paraná state, in southern brazil, using three production systems and seven soil tillage types, in a randomized block design. the following production systems were evaluated: (ps i) - ryegrass for soil cover (winter) and corn for grain production (summer); (ps ii) ryegrass for haylage/silage and corn for grain production; and (ps iii) - ryegrass for grazing and corn for grain production. seven types of soil tillage were evaluated in each system: (g1) - plow harrow in winter, depth 0.15 m; (g2) - plow harrow in winter and summer, depth 0.15 m; (plow) - disk plow, depth 0.20 m; (laser wing subsoiler) - subsoiler wing tips, to a depth of 0.45 m; (subsoiler) - subsoiler, depth 0.80 m; (aerator) - soil aerater aeromix？; and (nt) - no-tillage, where ryegrass was sown using a double disc and corn with a coulter. from each experimental plot soil blocks (0.20 x 0.15 x 0.07 m) were taken which were broken up by hand in their natural aggregates. then, the aggregates were air-dried for 24 h and passed through sieves with diameters of 12.5 and 19 mm. forty aggregates from each block were selected and tested for indirect tension to determine ts and quantify f. ts was influenced by the production systems and soil tillage types. the lowest and the highest ts values were found in the soil under grazing and the nt system, respectively. friability was less sensitive to differentiate production systems and soil tillage types.